The invention relates to a method for the spectrophotometric investigation of products of electrochemical reactions in which a solution containing at least one dissolved initial product is directed essentially axially towards a rotating disc electrode surrounded by an optically translucent ring, the flow being reversed at the rotating electrode into an outwardly directed radial flow, and the concentration of the products formed at the electrode being determined by passing monochromatic light through the radial product flow and the optically translucent ring and by measuring the light absorption, as well as to an apparatus for performing the method.
A method and an apparatus for the spectrophotometric investigation of electrochemically generated products is known from a publication in "Analytical Chemistry", Vol. 42, No. 4, pp. 551 and 552, 1970. A rotating electrode having a vertical rotation axis projects into a vessel below the surface of a solution used to perform the electrochemical reaction. The electrode has a working surface which is perpendicular to the rotation axis and which on the outer periphery of the working surface is surrounded by a number of optical fibres. The optical fibres are embedded in a cured synthetic resin and, after reversal in tapered manner into the direction of the rotation axis, pass together with the current lead to the electrode through the bearing of the rotating electrode and up to a light detector. Current lead and optical fibre cable are conducted through a stainless steel tubing providing the shaft which is guided in the bearings. An optical fibre cable for monochromatic light serving as the transmitter terminates at the bottom of the vessel and is directed coaxially to the rotation axis of the electrode with the optical fibres surrounding it. This apparatus is used employing the so-called lock-in technique. The electrical potential of the working electrode is cyclically changed with square pulses. In order to obtain reliable results with this technique, frequencies of at least approximately 10 Hz are usually selected. This technique and this apparatus permit approximate conclusions to be drawn on the course of chemical reactions. However, it is pointed out that considerable noise and low absorption values impair the precision of the investigations.